Commercial transport aircraft typically operate at cruise Mach numbers of about 0.85 or less. Although transporting passengers and cargo at higher speeds, such as transonic or supersonic speeds, can reduce travel time and increase revenue, flying at these speeds requires significantly more thrust. To generate more thrust, conventional transonic and supersonic aircraft typically use low bypass ratio turbofan engines or straight turbojet engines. These engine configurations generally have a high specific fuel consumption at cruise conditions that outweighs any increase in aerodynamic efficiency they may offer. This fuel consumption results in a net fuel efficiency for transonic and supersonic aircraft that is significantly lower than that of comparably sized subsonic aircraft. In addition, this low fuel efficiency can unfavorably increase atmospheric emissions.
Conventional transonic and supersonic aircraft engines typically operate at very high jet velocities when generating thrust for takeoff. These velocities can cause significant noise in airports and surrounding communities. One approach to reducing this noise is to lengthen the engine inlet and nozzle ducts and integrate noise abatement features with the ducts. One drawback to this approach is that such features typically increase the weight of the propulsion system, which in turn increases the structural loads on the wing and the susceptibility of the aircraft to wing flutter. Strengthening the wings to carry such additional loads results in increased structural weight, which further tends to increase the aerodynamic drag of the aircraft. Such an increase in aerodynamic drag increases fuel consumption, which in turn increases the amount of fuel that must be carried by the aircraft. Increasing the fuel capacity, however, further increases the structural weight of the aircraft, causing the design cycle to repeat.
Conventional commercial transport aircraft typically include a passenger cabin on an upper deck and a cargo hold on a lower deck. This configuration allows airlines to generate revenue by transporting both passengers and cargo over selected routes. On some routes, however, there may be a greater demand for passenger transport than cargo transport. On these routes, the airlines may accordingly prefer to use some of the space on the lower cargo deck for additional passenger seating.
One problem with adding passenger seating and/or other passenger facilities to lower decks is that lower decks typically provide insufficient standing height for passengers and crew. Another problem with using lower decks in this manner is that aircraft typically provide insufficient structure beneath lower-deck passenger seats to protect the passengers in the event of an impact such as a crash landing. Current regulations, for example, require at least 30 inches of compressible structure beneath a lower deck if the lower deck is to be used for passengers.
Many aircraft have retractable landing gears attached to their wings. These landing gears generally are movable between a static deployed position for supporting the aircraft on the ground and a static retracted position for reducing aerodynamic drag during flight. Because of high landing loads, these landing gears typically are attached to the wings with a substantial support structure. In addition to being very strong, such a support structure must also accommodate movement of the landing gear between the static deployed and static retracted positions.
Some conventional wing-mounted landing gears are pivotally attached between a rear wing span and a beam extending from the fuselage to the rear wing spar. Typically, the beam must be relatively large, and hence relatively heavy, in order to carry the high landing loads. One drawback to this approach is that the additional weight of the beam can adversely affect aircraft performance.
Other landing gears are attached to wings with a cantilevered beam extending aft of the rear wing spar. The cantilevered beam typically includes an aft trunnion support that is laterally offset from the beam centerline and configured to pivotally support an aft trunnion of the landing gear. One shortcoming associated with the cantilevered beam approach is that the lateral offset results in significant torsional loading of the cantilevered beam during landing. As a result, the cantilevered beam must be relatively large, and hence relatively heavy, in order to carry the torsional load without failure. As mentioned above, such additional weight can adversely affect aircraft performance.